An ICP emission spectrometer performs a quantitative or qualitative analysis of an element contained in a sample by determining the wavelength and strength of an atomic spectrum obtained by dispersing light which is emitted from the sample atom when this atom transitions to a lower energy level after being introduced into plasma and thereby excited.
As shown in FIG. 5, an ICP emission spectrometer includes: a plasma torch 310 for forming plasma, with an induction coil 311 wound around it; a sample introduction unit 340 for introducing a sample into the plasma torch 310; a gas flow control unit 350 for supplying plasma gas and cooling gas to the plasma torch 310 as well as carrier gas to the sample introduction unit 340, and for controlling their flow rates, a power supply unit 320 for supplying radio-frequency power to the induction coil 311; a control unit 330 for controlling each of these units; a spectroscope 371 for dispersing light from the plasma generated within the plasma torch 310; a detector 372 for detecting the dispersed light and for producing detection data representing the strength of the detected light; and a data processing unit 360 for processing the detection data (for example, see Patent Literature 1).
To perform an analysis of a sample using the ICP emission spectrometer 300, initially, while plasma gas and cooling gas are supplied at a predetermined flow rate from the gas flow control unit 350 to the plasma torch 310, a predetermined amount of radio-frequency power is supplied from the power supply unit 320 to the induction coil 311 in order to ignite radio-frequency induction plasma by a spark discharge. A stream of carrier gas is supplied from the gas flow control unit 350 to the sample introduction unit 340. The sample which is injected into and nebulized by this carrier gas is introduced into the plasma. Consequently, the excitation emission from the sample molecule occurs.
As the power supply unit, a self-oscillation radio-frequency power source as described in Patent Literature 2 has been proposed. In the ICP emission analyzer using this self-oscillation radio-frequency power source, an LC oscillation circuit is formed by a capacitor provided in the power source and the induction coil surrounding the plasma torch. The oscillation generated by this circuit produces a stable supply of radio-frequency power to the plasma torch.
The type of plasma torch is selected according to the kind or use of the sample to be analyzed. For example, a plasma torch for high-salt samples has a larger shape in its exit section than the standard plasma torch in order to prevent the adhesion of precipitated salts. A plasma torch for organic solvents has a smaller inner volume to allow for the vaporization of the sample within the plasma torch. Thus, different types of plasma torches have different shapes or inner volumes. Optimum values of the amount of radio-frequency power supply and the flow rate of the various kinds of gas also change depending on such differences. Accordingly, an operator should fit the ICP analyzer with the most suitable plasma torch for the analysis of the sample. The operator also sets, in the control unit, the type of plasma torch installed in the ICP analyzer. According to the setting, the control unit regulates the amount of power supply and the flow rate of the gas.